1. Field
Subject matter disclosed herein relates generally to positioning and, more particularly, to recovery from errors occurring in a process for obtaining a position fix.
2. Information
Satellite positioning systems (SPSs), such as the Global Positioning System (GPS) and the like, have enabled SPS receivers on mobile devices to generate position estimates for the mobile devices by processing signals received from transmitters aboard space vehicles (“SPS signals”). A position estimate generated by an SPS receiver may be referred to as a position fix. Typically, an SPS receiver will acquire SPS signals from four or more satellites of an SPS to generate a position fix. The SPS receiver may use these SPS signals to estimate distances (i.e., pseudoranges) to the four or more satellites. The pseudoranges may then be used, along with knowledge about the locations of the satellites, to generate the position fix for the mobile device.
When a position fix is desired, an SPS receiver of a mobile device may perform a search for SPS signals being received from space. If the SPS receiver has no knowledge of its current position or the current position of satellites of the SPS, this search may entail a full sky scan (which may be referred to herein as performing a search from a cold start) to acquire the satellites, which can be a very complex process. Because of its complexity, attempting to search for and acquire satellites from a cold start can consume significant energy and thus reduce battery life for a mobile device having an SPS receiver. In addition, in mobile devices having limited processing power, searching for SPS signals from a cold start can be very time consuming and thus delay the generation of the position fix. An untimely or delayed position fix may negatively impact applications which rely on position knowledge.
In some systems, assistance data may be used by an SPS receiver to reduce the complexity of the search for SPS signals. If assistance data is used, an SPS position fix may be achieved more quickly and with less power consumption. By reducing power consumption, battery life may be extended. Assistance data may include, for example, a rough estimate of a current location of a mobile device, an estimate of SPS time, Doppler search window information, almanac and/or ephemeris data, as well as other forms of information. This assistance data may be obtained from various sources including, for example, a remote location server accessible through a wireless communication network, a wireless base station or access point associated with wireless communication network, information stored within the mobile device itself, and/or other sources.
While assistance data may allow a position fix to be obtained more quickly and with less energy expenditure, sometimes assistance data may be inaccurate or erroneous. As will be appreciated, the use of faulty assistance data can negatively impact the accuracy of a resulting position fix. In addition, it is often difficult to determine the accuracy of assistance data before the data is used. Any resulting errors in a position fix, therefore, may not be detected until one or more location-based applications that use the position fix data malfunctions. It would be desirable to have techniques and structures that are capable of identifying and recovering from position fix errors in a more timely and/or efficient manner.